1. Field of the Invention
The present invention relates to a liquid ejection apparatus and an image forming apparatus, and more particularly, to a liquid ejection apparatus and an image forming apparatus using same, such as an inkjet recording apparatus, which is suitable to an application for ejecting a high-viscosity liquid in the form of very small liquid droplets.
2. Description of the Related Art
As a method of driving ejection in order to eject very small liquid droplets from an inkjet head, a method has been proposed in which the internal volume of an ink chamber is firstly increased, and then allowed to revert to its original state, thereby pushing the ink out from the nozzle, whereupon, before the ink thus pushed out is severed from the nozzle, the internal volume of the ink chamber is increased again in order to sever the ink from the nozzle (see Japanese Patent Application Publication No. 2-184449).
Japanese Patent Application Publication No. 2-184449 makes no mention of the ink viscosity. If the severance operation described above is not performed when high-viscosity ink is ejected, then sufficient negative pressure is not produced in order to “tear off” the liquid after pushing out the liquid because the applied pressure wave is attenuated rapidly due to the high viscosity of the ink, and hence the liquid stretches into a long column and it becomes difficult to form a very small liquid droplet. Therefore, in order to eject a high-viscosity liquid as a very small liquid droplet, then desirably, a waveform which tears off the liquid column (a waveform for severing the ink column) is added.
However, although Japanese Patent Application Publication No. 2-184449 discloses an ink severance operation, it does not refer to the timing of the effective increase in the internal volume of the ink chamber in the severance operation. In the case of a high-viscosity liquid, since the applied pressure wave attenuates rapidly, then unless a pull-back operation is performed at a specific timing in order to create a negative pressure which tears off the liquid column, it is not possible to obtain a negative pressure of a sufficient magnitude.